Foam-in-place packaging is a known technique for producing cushioning packaging for fragile articles which are to be shipped. Foam-in-place packaging comprises generating foam cushioning on an as-needed basis while the article to be protected is being packaged. In general, foam-in-place packaging employs foamable compositions which are produced by bringing together two or more precursor chemicals that react and form foam when mixed together. The chemicals are generally selected from among those chemicals which when mixed form polymeric foams that harden upon curing. For example, a liquid polyol-containing precursor and a liquid isocyanate-containing precursor may be mixed and reacted to form a polyurethane foam. The resulting foam occupies a volume which is many times the volume of the liquid precursors.
One technique for foam-in-place packaging is to place the article to be packaged in a container, and then to place one or more flexible plastic bags containing a foamable composition into the container. The foamable composition expands to cause the bag to fill the void space between the walls of the container and the article, and then hardens. The result is a foam cushion that conforms closely to the shape of the article and the container, and thereby cushions and protects the article. This technique is referred to herein as the foam-in-bag technique.
A number of automated devices have been developed for rapidly making a relatively large number of bags for foam-in-bag packaging, and are assigned to the assignee of the present application. Exemplary devices are described and claimed in U.S. Pat. Nos. 4,674,268; 4,800,708; 4,854,109; and 5,376,219. Because these devices mix the precursors together as they are placed in the bags, the resulting bags must be placed in the containers with the articles immediately. Accordingly, these devices are particularly suitable for use in situations where it is desirable and feasible to make the bags containing the foam precursors at the location where articles are being packaged.
However, in certain applications, it may not be desirable to employ such automated devices to make foam-in-bag packaging directly at the packaging location. Accordingly, the assignee of the present application has developed a bag for foam-in-bag packaging use in which the precursor chemicals are contained in a bag and kept separated from one another until it is desired to form a foam cushion from the bag. At that time, the bag may be manipulated to cause breakage of a frangible membrane that separates the two precursors and to mix the precursors together. The bag is then placed into the packaging container adjacent the article to be protected. The precursors react to form foam, and the bag expands to fill the void space and cures to form a cushion. The bag is described and claimed in co-pending U.S. patent application Ser. No. 09/042,444 entitled "Foam In Bag Packaging System and Method for Producing the Same" and filed concurrently herewith, which is assigned to the assignee of the present application, and the disclosure of which is incorporated herein by reference.
It will be appreciated that the volume of foam produced in the bag is influenced by a number of parameters, including the masses of the two precursors, the ratio of the masses, and the temperature of the precursors. Additionally, the speed of the foam-forming reaction depends on the temperature of the precursors, generally increasing with increasing temperature. The masses of the precursors and their ratio can be accurately controlled in manufacturing the bag. However, the temperature of the precursors is influenced by the environment in which the bags are kept prior to use. It will be appreciated that without some means of controlling the temperature of the bags, variability in temperature will occur and result in inconsistent foam expansion from one application to another, with resultant inconsistency in packaging characteristics.